This invention relates to a syringe for drawing and releasing a vacuum so that the syringe may be used for obtaining a sample of tissue for a biopsy.
A technique which is useful for obtaining tissue samples for a biopsy is known as fine needle aspiration. When a physician suspects tissue observed by x-ray, ultrasound, or palpation may be cancerous, it is usually desirable to obtain a sample of the tissue for microscopic examination. The fine needle aspiration technique is used, for example, for sampling what appear to be lung lesions, lumps in the breast, dense prostrate tissue, or other anomalous portions of body organs.
A hollow needle or cannula is inserted, typically through the skin, so that the tip of the needle is in the suspect tissue. The plunger of the syringe is then withdrawn to pull a small amount of tissue into the hollow needle. The needle is withdrawn and the tissue sample discharged onto a slide for examination. Such aspiration of tissue into the needle may be performed in several locations in suspected tissue with a single insertion of the needle into the body.
In a typical examination using fine needle aspiration, the physician may palpate a breast to isolate and grasp a lump with one hand, and with the other hand guide the needle of an aspiration syringe into the lump. A "control" syringe may be used with finger grips on the barrel and plunger of the syringe so as to draw a vacuum in the barrel once the needle is in the lump.
At that point it becomes desirable to release the vacuum in the syringe. Failure to do so when the needle is withdrawn from the body may result in the tissue being drawn through the needle into the barrel of the syringe, where it may be lost and unavailable for biopsy. The vacuum in the barrel should not be released by simply pressing the plunger forward again since this could prematurely discharge the tissue from the needle, even before it is withdrawn from the body.
It is also desirable to introduce air into the syringe so that when the plunger is returned toward the end of the syringe, pressure in the barrel discharges tissue onto a slide for microscopic examination. It is also important for some fine needle aspiration procedures that the physician be able to operate the device entirely with one hand, at least until a sample is obtained, so that the other hand may be used to know or hold the position of the lump. Obtaining a sample of breast tissue is a good example. Breast cancer is of increasing concern for women. Improved methods for diagnosis are essential.